Allelochemicals or secondary metabolites in many plants can affect seed germination, growth and development, density, and distribution of plants, and are an important source for the development of herbicides (Cespedes et al., 2014). A large number of natural products having herbicidal activities are being screened and tested throughout the world by researchers. For example, Conyza canadensis, Cephalotaxus sinensis, Flaveria bidentis, Partheniumhy sterophorus, corn protein powder and other plant extracts have been confirmed to contain herbicidally active ingredients (Gao Xingxiang, et al., 2010; Ma Shujie et al., 2016; Li Jianqiang, et al., 2012; Chen Yebing et al., 2010; Yang Jian and Lu Changyi, 2010).
Only a few plant derived herbicides, however, are registered or approved for use. These include cinmethylin, a highly effective broad-spectrum herbicide successfully developed as a derivative of cineole extracted from plants. After entering into plants such as rice, soybean, cotton, and peanuts, this compound can be metabolized into a hydroxyl derivative, which then binds to glycosides in the plants to form a conjugate, thus losing its toxicity (Grayson et al., 1987). Another successful example of herbicides developed from the plant allelochemicals is the triketone herbicides, specifically sulcotrione and mesotrione, with leptospermone developed as a lead compound. Leptospermone is a highly effective inhibitor of Phydroxyphenyl-pyruvate dioxygenase (HPPD). When used for pre- and post-emergence treatment, certain grass (Poacea) and broad-leaved weeds develop symptoms of albinism; however, maize is resistant to leptospermone (Mitchell et al., 2001).
The development of commercially viable, highly effective, broad-spectrum and safe plant-derived herbicides remains an arduous and lengthy process, and it is necessary to expand the plant species to be screened, and make structural derivatives of natural compounds having herbicidal activities.
Fatty acid herbicides are well known in the art and are generally considered to be environmentally friendly. Fatty acid herbicides are typically supplied as concentrates that are diluted with water and applied as an oil-in-water emulsion. These concentrates usually contain the fatty acid active ingredient and emulsifying agents including surfactants and oils such as sodium dodecyl benzene sulfonate (ABS).
Caprylic acid, also referred to as n-octanoic acid, and widely found in Myristica fragrans, lemongrass, apples, coconut oil, wine, and hops etc., has a molecular formula of C8H16O2 and is a colorless transparent oily liquid having a sweat smell. It is mainly used in the production of dyes, drugs, spices, plasticizers, lubricants, or as preservatives and fungicides, etc. (Parag et al., 2014; Salimon et al., 2012; and Liu et al., 2008).
U.S. Pat. Nos. 4,975,110; 5,106,410 and 5,098,467 disclose fatty acid herbicidal compositions that contain C8-12 fatty acids, a surfactant and water with pelargonic acid being a preferred fatty acid herbicide. U.S. Pat. Nos. 5,098,468 and 5,035,741 also disclose fatty acid herbicidal compositions that contain C8-12 carbon fatty acids, an oil component, an emulsifier and water. Single phase concentrates are disclosed in U.S. Pat. Nos. 5,098,468 and 5,035,741 that contain the fatty acid(s), oil and emulsifier.
U.S. Pat. No. 5,919,734 discloses herbicides comprising fatty acids and a compatible oil component.
Fatty acid herbicides include fatty acid esters of C6-C20 monocarboxylic acids such as those disclosed in U.S. Pat. No. 5,284,819.
Additionally, fatty acid salts such as those disclosed in U.S. Pat. Nos. 2,626,862; 4,975,110; 5,035,741, and 6,930,075 can be employed as fatty acid herbicides.
However, no water soluble fatty acid salt has been found to be an effective herbicide alone without another petrochemical-based herbicide (e.g. glyphosate), or without an emulsifier, or without an oil component.
Caprylic acid was mentioned as a component in prior art herbicidal compositions (e.g. U.S. Pat. Nos. 4,031,140; 4,663,364, disclosing a herbicidal powder; U.S. Pat. No. 5,919,734, disclosing an oil-based fatty acid herbicidal composition; U.S. Pat. No. 6,930,075, disclosing a fatty acid-based herbicidal composition; and U.S. Pat. No. 9,578,877, disclosing cocoalkylpolyamine alkoxylates as agents for high strength herbicide compositions, where caprylic acid is mentioned as a supplement.
Caprylic acid, however, has never been used as a primary agrochemical active ingredient or herbicidal ingredient prior to the instant invention. Further, no disclosure of the isopropyl amine salt of caprylic acid as an effective herbicidal agent was found in the prior art.